DNA Replication Flashcards
In what direction is DNA synthesised in?
Always synthesised in the 5’ —> 3’ direction, the parental templates run in the 3’ —> 5’ direction
What is involved in eukaryotic DNA replication?
Multiple large linear chromosomes (23 pairs in humans), multiple origins of replication, bidirectional
What is needed to make a DNA copy?
Progressive addition of new nucleotides (DNA polymerase III), a starting point for nucleotide addition (primase), unwinding of the helical double-stranded DNA (helicase), release of tension generated by unwinding DNA helix (topoisomerase), prevention of unwound DNA (single stranded DNA binding protein), removed RNA primer and filled with DNA nucleotide (DNA polymerase I) ends of newly synthesised fragments joined together (DNA ligase)
How is replication semi-discontinuous?
Leading strand: continuously synthesised in 5’—>3’ direction
Lagging strand: discontinuously synthesised in 5’ —> 3’ direction forming Okazaki fragments
What is Primase?
Enzyme that makes an RNA primer = starting point for DNA polymerisation
What happens in DNA Polymerase III
Enzyme synthesises a new DNA strand by adding nucleotides complementary to the parental template strands.
What happens in DNA Polymerase I?
Removes RNA primers and fills the gap with DNA nucleotides (DNA polymerase)
What happens in DNA ligase?
Joins the newly synthesised Okazaki fragments (lagging strands) together creating phosphodiester bonds. Also joins newly synthesised fragments from the multiple replication bubbles (including leading strands)
What activities does DNA Pol I carry out?
RNase Activity: degrades RNA part of DNA:RNA hybirds
DNA Polymerase Activity: synthesis DNA by adding nucleotides
Where can DNA errors be repaired?
During replication (exonuclease) or after replication (endonuclease)
Repair of DNA error during DNA Replication
DNA replication shows high accuracy and has a proofreading mechanism. Incorrect bases are removed by a 3’ to 5’ exonuclease activity of DNA Pol III
Repair of DNA errors after DNA replication
Removed by an endonuclease. If not corrected the DNA error becomes part of the DNA template -> permanent DNA change
What is polymerase chain reaction?
In vitro method of making multiple DNA copies so that there is enough DNA material to work with. Only targeted regions will be copied
What components are involved in PCR?
DNA template: complementary nucleotides matched
Primers: provides free ‘3 OH group, defines region of DNA that will be replicated
DNA Polymerase: enzyme which adds nucleotides and joins them
dNTPs: free nucleotides
